The present invention relates to the medical diagnostic imaging arts. It finds particular application in conjunction with a clinical medical radiographic and fluoroscopic x-ray system and will be described with particular reference thereto. However, it should be appreciated that the present invention may also find application in conjunction with other types of imaging systems and applications.
Sepsis control and access to the full perimeter of the patient are two prime requirements for surgical and interventional procedures performed in, but not limited to, hospital operating rooms, health care facilities that utilize minimally invasive surgical technology, and in dental operatories. The above requirements have almost always compromised the convenience of use and the imaging performance delivered from classical surgical "C-Arm" x-ray systems, both fixed and mobile.
In particular, traditional x-ray systems are designed to be used with the x-ray image receptor positioned as close as is practical to the patient's skin. Traditional systems using cassettes and intensifiers typically demonstrate 1 to 2 line pairs per millimeter (lp/mm) fluoroscopic spatial resolution at a dose rate of 10 to 30 nGy (.about.1 to 3 .mu.R) per video frame at the entrance of the image receptor for x-ray tube focal spots measuring between 0.5 and 0.9 mm. Substituting a flat plate matrix imager and using the traditional x-ray geometry results in about the same performance when these devices are fully developed. The spatial resolution for high photon flux radiographic recording of fluoroscopic images is typically between 3 to 5 lp/mm.
The traditional viewing or recording film image magnification ratio as it relates to the anatomy of interest is typically 1.2 to 1.4:1. If the traditional receptor is moved away from the patient's skin, the magnification ratio increases and this disadvantageously causes the always-present penumbral unsharpness to be magnified to the point where subtle anatomic margins begin to disappear. Another consequence of moving the traditional receptor some distance away is the reduced amount of patient anatomy that can be captured at the receptor.
In a known highly-specialized application that is used specifically for imaging the relatively small field size associated with a mechanical heart valve, a "microfocus" x-ray source is employed to project images on an image intensifier located at a great distance away from the patient. The "microfocus" source is utilized to prevent unsharpness in the magnified image. The sole purpose of magnifying the image of the heart valve is to permit assessment of its mechanical integrity, specifically the detection of small cracks in the welding that are more easily seen using magnification. This specialized imaging system demonstrates the well-known limitations in kilowattage presented by all microfocus x-ray tube designs where the finite melting point of tungsten anodes effectively eliminates having practical and affordable stop-motion microfocus magnification radiography in clinical settings.
Accordingly, it has been considered desirable to develop a new and improved image minifying radiographic and fluoroscopic x-ray system which meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.